Space-time encoding is one of the important methods that can raise performance of a wireless communication system effectively. There are two branches of the space-time encoding, one is layered space-time encoding and the other is space-time encoding based on transmitting diversity. The space-time encoding based on transmitting diversity can be further divided into two kinds: space-time block encoding and space-time trellis encoding.
Along with the development of high-speed wireless communication technology, the signal transmission bandwidth and rate is increased continuously, which means that time for transmitting a data symbol is shorter and shorter. Therefore, time delay spread of a wireless transmission channel cannot be neglected, that is, the channel frequency selective fading is getting worse.
The prior space-time encoding and decoding schemes are designed based on a flat fading channel. When the schemes are used for a frequency selective fading channel, the performance becomes worse obviously, and it is too complex to implement when improving performance of the algorithm.
In a multi-user frequency selective fading channel, since Inter-Symbol Interference (ISI) and Multiple Access Interference (MAI) exist at the same time, implementation of space-time encoding and decoding has great difficulty. Some effective methods for counteracting ISI and MAI on a frequency selective channel, such as equalization, joint detection method etc., become very complex or even failure if space-time encoding is involved therein.
In the 3rd Generation Partnership Project—Time Division Duplex (3GPP-TDD) system, the prior space-time encoding and decoding scheme used for a multi-user frequency selective fading channel only performs space-time encoding for the basic common control channel, but in the 3rd Generation Partnership Project—Frequency Division Duplex (3GPP-FDD) system, space-time encoding is employed for most channels. The 3GPP-TDD space-time encoding scheme first takes a symbol as an encoding and decoding unit, later it takes a half of symbols of a data field as an encoding and decoding unit. Since these schemes have many changes that bring more complex compared with the schemes in which space-time encoding is not employed, the space-time transmission diversity (STTD) scheme is discarded in 3GPP-TDD v4.3 and space code transmission diversity (SCTD) scheme is applied. Although the reception processing procedure is simplified with the SCTD, more channel resource is occupied and more channels are employed; it is difficult to be applied to other kinds of channels, and also it is impossible to be applied on the multipath diversity situation.
There is a space-time encoding and decoding scheme that transforms high-speed data to multiple parallel low-speed data and transmits them on multiple channels, but really this is a space-time—orthogonal frequency division multiplexing (ST-OFDM) method that would thoroughly change the signal structure and system on the physical layer, so it is greatly limited in practical use.
In summary, the space-time encoding and decoding method is important to improve performance of a wireless communication system. Usually, a symbol or a string of symbols are used as a processing unit for encoding and decoding, but under the condition of a frequency selective fading channel, improvement of performance is limited by the calculation complexity.